1. Field of the Invention
This invention relates to computer disk drives and particularly relates to a technique for providing start up power to individual spindle motors of a plurality of disk drives.
A disk drive is a mass data storage peripheral unit employed with a digital computer. In a large computer installation, there may be two or more and typically up to eight disk drives employed. In order to facilitate rapid data storage and retrieval from moveable disks, a disk normally propels the storage disks continuously throughout the period of operation of the computer. The motor coupled to the spindle supporting the disks is called a spindle motor.
Generally about ten to fifteen seconds are required to bring an idle spindle motor up to operating speed. The starting torque of a typical spindle motor is such that 35 to 50 amperes of current may be drawn from the electrical power source. If as many as eight spindle motors are started simultaneously, an undesired peak load of as much as 400 amperes can be drawn for a short period of time. Such a peak load can cause damage to the power source and to power carrying cables. Therefore, means are needed to start up the spindle motors of a disk drive which avoids power source overload and consequent damage.
2. Description of the Prior Art
Disk drive sequencing is well-known. In one common technique, a three wire control circuit is required. Basically, the technique requires a Sequence "Pick In" line connected in series with a Sequence "Pick Out" line and a Sequence Enable (SE) line. (Additionally a ground or common is needed.) Through the SE line, a master controller issues a signal to supply AC power to a string of drives. The SE line designates which drive is started first. The SE signal to a particular drive causes the Sequence Pick In/Sequence Pick Out lines to be interrupted thereby preventing any other disk drive from powering up.
The above technique has inherent limitations. It is dependent upon an external controller and also requires at least three control signal lines for proper operation. Moreover, it is ill-adapted to make use of the independent decision-making capabilities of disk drives. Present state of the art disk drives now incorporate preprogrammable control units employing a microprocessor. New start up control techniques are needed in order to take advantage of the availability of independent decision-making capabilities of each such disk drive, namely to take advantage of the availability of the microprocessing unit and programmable functions therein.